1. Technical Field
The present invention relates to a plastic lens and a method of manufacturing a plastic lens.
2. Related Art
Plastic lenses have rapidly prevailed in the filed of spectacle lenses, and account for a large share thereof, because they are lightweight, excellent in formability, processibility, tinting properties and the like, and are resistant to breakage and highly safe as compared with glass lenses. Also, in recent years, materials having a high refractive index such as thiourethane based resins and episulfide based resins have been developed for the purpose of meeting further needs of reduction in thickness and weight saving. On the other hand, because plastic lenses are readily scratched as compared with glass lenses, a hard coat layer is generally formed on the surface of the plastic lens to improve the surface hardness. Additionally, for the purpose of preventing the surface reflection, an antireflection film is formed by vapor deposition of an inorganic material on the upper face of the hard coat layer, and still further, for the purpose of improving the water-repelling and oil-repelling performances of the surface, an antifouling layer composed of an organic silicon compound containing fluorine is formed on the upper face of the antireflection film. Hence, the plastic lenses have further progressed as highly functional lenses by means of technological innovation of the surface treatment.
However, the plastic lenses involve the problem of low heat resistance, and in particular, as the plastic lens resin material has higher refractive index, the heat resistance is liable to decrease. Additionally, the inorganic antireflection film among the surface-treatment layers, in particular, can not follow the deformation due to thermal expansion of the plastic lent being the substrate. As a consequence, problems of occurrence of fogging and crack may be raised, and such problems tend to be prominent as the plastic lens has higher refractive index.
Meanwhile, the inorganic antireflection film is formed by a vacuum evaporation process, therefore, it generally has a high film density, and has a property to shield the hard coat layer being a substrate layer from factors which may deteriorate the durability of the plastic lens such as oxygen, moisture and ultraviolet light outside of the lens (protective effect). According to such an inorganic antireflection film, even though the hard coat layer was formed as the substrate layer using a coating composition which includes titanium oxide having an anatase crystal structure as a principal component accompanied by low light resistance, the durability can be secured to some extent. In contrast, according to the antireflection film composed of an organic thin film has relatively low film density as compared with the inorganic antireflection film, and has a structure having pores, such a protective effect as that of the inorganic antireflection film can not be achieved. Therefore, when the hard coat layer was formed using a coating composition which includes titanium oxide having the anatase crystal structure as a principal component, the durability becomes so unsatisfactory that the hard coat layer being the substrate layer is demanded to have higher durability.
To meet such demands, techniques to form a hard coat layer using a coating composition which includes metal oxide fine particles including titanium oxide having a rutile crystal structure as a principal component were proposed. Because titanium oxide having low photoactivity is used in this hard coat layer, the durability can be improved as compared with known titanium oxide having an anatase crystal structure, while maintaining high refractive index (for example, see JP-A-11-310755).
However, when an antireflection film composed of an organic thin film was formed on the upper face of the hard coat layer which includes such rutile type titanium oxide, the hard coat layer may not have sufficient durability, and further improvement of the durability is required. Thiourethane based resins and episulfide based resins used in the plastic lens substrates having a high refractive index predominating in recent years have a sulfur atom on its main chain skeleton. This sulfur atom hardly causes an interaction with a polar group such as a silanol group in the organic silicon compound that is present in the hard coat layer, and a property to inhibit the hardening of the hard coat layer itself is found, therefore, achievement of adhesion between the hard coat layer and the plastic lens substrate tended to be difficult. In particular, when an antireflective layer composed of an organic thin film was formed on the upper face of the hard coat layer, the adhesiveness with the plastic lens substrate may be insufficient, and in addition, water and oxygen passed through the organic thin film may deteriorate the hard coat layer. Thus, according to the construction having an antireflective layer composed of the organic thin film was provided on the upper face of the hard coat layer, to achieve sufficient durability (adhesive and protective effect) was difficult.
Furthermore, demands for tinted lenses among the plastic lens for spectacle lenses are great, and in general, tinting of plastic lens substrate by a disperse dye has been carried out. In this instance, the dye is present on the plastic lens substrate surface, therefore, adhesiveness between the hard coat layer and the plastic lens substrate is deteriorated as compared with untinted lenses. The disperse dye present on the plastic lens substrate surface is found to have a property to be altered predominantly by ultraviolet ray or oxygen. Particularly, when an antireflective layer composed of an organic thin film was provided on the upper layer of the hard coat layer, alteration is more likely to occur, which may be the grounds for deterioration of the adhesiveness between the hard coat layer and the plastic lens substrate.